Developing the DIY "Champ" for first time builders

[ToneMerc]

IMHO, that 60mA PT is too small for anything larger than a 6V6.

Here's a my minimum PT HT current rating rule thumb for a single tube.

6V6= 60-70mA
6L6/EL34= 85-95mA
KT66/KT88= 100-115mA

If you want a PT that will run just about any single tube, find one with at least 120mA.

I did have Heyboer spec out an upright Champ PT that would run all tubes abd rectifiers. IIRC, the mounting centers were pushed another 1/2 inch or so. This about as big as can be designed on that tiny frame size.

320-0-320@110mA
5V@3A
6.3V@2A

TM

[angelodp]

rj, are we talking an expansion of the chassis or just a bigger iron.

ange

[RJ Guitars]

rj, are we talking an expansion of the chassis or just a bigger iron.

ange

For those that want bigger iron - I would make it available with a bigger chassis. 14.5 x 7.5 x 2 (i ordered the blanks last week). For those that really like a challenge I suppose they can put the big iron on the little chassis but I consider it a bit crowded.

I'll offer three iterations:
Basic -- Less than $100
Upgraded -- Less than $135 (Edcor transformers for 6V6GT)
Supersize -- Less than $?? Mega transformers for up to a KT-88

rj

[surfsup]

RJ, that sounds great. Super-size me with fries!

Also, are you planning on predrilling all the chassis? I am wondering if I should just drill it myself and get a blank from you. the reason is I plan to add another 12ax7 before the PT and a tube recto, so I'd want it to take that into consideration.

[Zippy]

Thoughts...

We are already running low voltages for the big tubes (which I like) so I see little need for 5V rectifier current to implement a tube recitifier. Of course, if it's a stock configuration, no worries - I just wouldn't add it if not already there.

At that voltage, I'm still wondering if we need 15W OT or whether the original is sufficiently beefy.

My driver? Getting the most into and out of the smallest combo that will house a 10" speaker.

g

I've had a couple inquiries now about a Super Size version of this. I am on the verge of ordering a half dozen sets of iron but I think they may require more real estate than the little brother... any thoughts?

I was thinking:

PT
230-0-230 @ 150mA
6.3v @ 3A
5v @ 2A

OT
15 watts SE

rj

[RJ Guitars]

Thoughts...

We are already running low voltages for the big tubes (which I like) ... g

I was thinking:

PT
230-0-230 @ 150mA
6.3v @ 3A
5v @ 2A

rj

Then I starting researching and found something darn close... http://edcorusa.com/products/670-xpwr074_120.aspx

I was wondering where we want the B+ voltage to end up for the bigger tubes.

I was also wondering where we might want the impedance to end up for the bigger tubes? http://edcorusa.com/products/537-gxse15-8-5k.aspx

rj

[telentubes]

Can you give us a general comparison of the "upgraded" and "super". What does the "super" offer tonally that the "upgraded" won't have? I have a use for a small amp with rich beautiful cleanish tone, so would want to go in that direction. I don't need volume as much as tone.

(Seems like, with all these choices, I may need one of each).

[Firestorm]

I was wondering where we want the B+ voltage to end up for the bigger tubes.
rj

How about this one? http://edcorusa.com/products/655-xpwr061_120.aspx

Run it tube rectified for 6V6/SS rectified for bigger tubes. Run a separate set of SS diodes off the secondary and just toggle between the two B+ values.

OT should be 20Wish to handle 6550/KT88. Primary impedances are all over the place with the tube types being talked about. Best choice would be an OT with multiple secondary taps so we could better match the impedance for the tubes types. Harder to source. Don't think Edcor does one like that.

[Zippy]

Can you give us a general comparison of the "upgraded" and "super". What does the "super" offer tonally that the "upgraded" won't have? I have a use for a small amp with rich beautiful cleanish tone, so would want to go in that direction. I don't need volume as much as tone.

(Seems like, with all these choices, I may need one of each).

Running the larger tube at the same volume should mean more headroom. Running it at the same amount of distortion should translate to louder.

Your choice as to where you dial the knob.

[Zippy]

Run it tube rectified for 6V6/SS rectified for bigger tubes. Run a separate set of SS diodes off the secondary and just toggle between the two B+ values.

Why? What do you hope to gain from adding that level of complexity?

OT should be 20Wish to handle 6550/KT88. Primary impedances are all over the place with the tube types being talked about. Best choice would be an OT with multiple secondary taps so we could better match the impedance for the tubes types. Harder to source. Don't think Edcor does one like that.

Again, I'm asking for someone with some DATA on these tubes. Running at low voltage should keep the output pretty low - even for an KT88. I don't know and that's why I'm looking for something concrete.

If we are trying to make a compact and simple SE combo, let's not burden ourselves with anchors for trannies if we don't need too.

[rp]

that edcor 15W will likely handle anything. They look way over built and are M6, plus, I didn't check, but if it 15W 20-20k Hz then at 80-20K Hz it'll be like 25W anyway. Please correct me if I'm wrong here. Point is to keep this thing simple and cheap right?

[Firestorm]

Run it tube rectified for 6V6/SS rectified for bigger tubes. Run a separate set of SS diodes off the secondary and just toggle between the two B+ values.

Why? What do you hope to gain from adding that level of complexity?

Keep the 6V6 happy; provide more juice for 6L6,6550,KT88. Two diodes and a switch; how complex is that?

OT should be 20Wish to handle 6550/KT88. Primary impedances are all over the place with the tube types being talked about. Best choice would be an OT with multiple secondary taps so we could better match the impedance for the tubes types. Harder to source. Don't think Edcor does one like that.

Again, I'm asking for someone with some DATA on these tubes. Running at low voltage should keep the output pretty low - even for an KT88. I don't know and that's why I'm looking for something concrete.

If we are trying to make a compact and simple SE combo, let's not burden ourselves with anchors for trannies if we don't need too.

6550A/pentode wired/400V plate/load resistance 3K = 20W Po.

6550A/pentode wired/250V plate/load resistance 1K5 = 12.5W Po.

6L6GC/pentode wired/350V plate/load resistance 4K2 = 10.8W Po.

6V6GTA/pentode wired/315V plate/load resistance 8K5 = 5.5W Po.

A well designed 15W OT would probably suffice. It's the broad range of load resistances I was thinking to accomodate. Any one would "work," but with different tone.

[mike9]

Correct me if I'm wrong, but if you are an experienced builder why would you even bother with a kit like this?

Sounds to me like the goal is being derailed somewhat. The original idea of a "beginner" amp kit has now turned into a Swiss Army Knife type of science project. I'm all for a SE 6L6, but for $100 I figure what I learn on the champ will be translatable to a bigger build later on. Just my two cents -

[angelodp]

Not derailed, simply expanded. I say we are lucky that there so many furtive minds here that are passionate about amp work, and simply crave the experimentation and knowledge. It seems that Leo Fender made changes to his amps within a specific model, only a serial number apart. Bravo rj et-al for having a broad selection to play with.

ange

[Zippy]

Thanks for the values regarding the output tubes.

Keep the 6V6 happy; provide more juice for 6L6,6550,KT88. Two diodes and a switch; how complex is that?

You're forgetting the socket and tube... In truth, isn't the voltage already in the keep-the-6V6-happy range and a lil' low for the Big Guys? If you want to drop voltage, you can similarly wire for SS rectification and add a "choke resistor" to drop some series voltage.

g